Washington (CNN) — A prominent atheist group is using next month’s Democratic National Convention to take aim at the presidential candidates’ religion, putting up billboards targeting Mormonism and Christianity in Charlotte, North Carolina.

“Our political system is rife with religion and it depends too much on religion and not enough on substance,” said David Silverman, president of American Atheists, sponsor of the ads.

“Religion is silly and religion has components that are inherently divisive. … There is no place for any of that in the political system,” he said.

The billboards go up Monday in Charlotte and will stay up for a month at a cost of roughly $15,000. The Democratic convention runs September 3-6.